The amino acid sequences of two closely related peptides from Gila monster (Heloderma suspectum) venom have been determined. Helospectin I is a 38 residue peptide and helospectin II is a 37 residue peptide identical to helospectin I except that it lacks serine 38. Helospectins are pancreatic secretagogues with structures similar to vasoactive intestinal peptide and other members of the glucagon superfamily (glucagon, secretin, somatoliberin, gastric inhibitory peptide, PHI). Since members of the glucagon superfamily have different biological actions, it is possible that helospectin is more closely related to a mammalian peptide awaiting discovery. The amino acid sequences of five structurally related peptides from bumble bee (Megabombus pennsylvanicus) venom have been determined. The 17-residue peptides, which we have named bombolitin I-V, lyse erythrocytes and lysosomes, release histamine from mast cells and stimulate phospholipase A2 from difference sources. While the bombolitins represent a unique structural class of peptides, they have biological properties very similar to other structurally unique peptides from insect venoms: melittin from honey bee venom, mastoparan from wasp venom, and crabrolin, a peptide we recently isolated from European hornet venom. This unusual circumstance-peptides with different amino acid sequences having similar biological properties--may be a manifestation of their amphiphilic nature, a structural property these peptides have in common. The amino acid sequences of three peptides from the skin of Rana pipiens have been determined. The structurally similar 24-residue peptides lyse erythrocytes and release histamine from mast cells with a potency at least 10 times higher than the bombolitins or crabrolin. Several peptides have been partially purified from the venom of the snake oxyuranus scutellatus which interact specifically and competively with calcium binding channels of the dihydropyridine category. Finally, all the common dansyl amino acids have been separated in a single high performance liquid chromatographic run.